Phonon/Akademy2012BoF

We've planned a small BoF for Akademy 2012. You can view the schedule at Akademy/2012/Monday.

Agenda

• Qt5 and Phonon
  • Integration with Qt5
  • Discussion about qt-project.org
• Windows
• Phonon 5
  • Current Issues
  • Phonon 5 preliminary designing
• Capture, Recording
  • Phonon Encoder, formats, api
  • Capture issues

Notes

• Qt-project.org
  • Tabled for now, revisit in a few months if the CLA changes
  • Where to get Phonon for Qt5
    • Won't be part of 5.0, will be available soon after
  • Source code compatability

Current Issues

• State machine
  • Something linear like GStreamer's
  • Separate error reporting
• KDELibs: Can't use phonon because when you press play, the decoding is done again, makes it impossible for small sound samples.
  • tdfischer's sample cache API
• aboutToFinish Signal
• Which level does phonon even live at?
  • Higher level: queue these things and play them
  • Lower level: mixer API? sound sample cache API?
  • Split the queueing stuff into a separate MediaQueue class, limiting the MediaObject to single playback only
  • Volume controls: exactly one application needs it, shouldn't have it
    • Volume keys sometimes results in two volume OSDs: one from Phonon/Amarok, one from KMix.
    • Quicktime: Only soft volume, DirecShow: Only soft volume
    • Should only control the application volume, as players expect a volume control. No hardware mixers.
      • todo: review volume control guidelines for gnome, windows, etc
    • You should only want to change the volume you are outputting to the sink
• Crossfading? Yes, but low priority.
• Playback rate. Yes, it is trivial to implement. Maybe an option to keep the pitch.
• Inserting/removing devices is pretty common.
• Effects API?
  • Do we need a generic effects API?
  • Equalizer is needed. Perhaps thats all we need.
• Graph structure is broken. Very broken. Stop laughing. Having an API to do a graph about frameworks that do graphs in different ways is dumb. Only GST seems to have a proper graph. Quicktime is weird, DirecShow is not a graph.
  • <j-b> Remove the graph. If you need it, phonon is not right.
  • What isn't using phonon and why?
    • Telepathy, which is using GStreamer
    • Games don't use it because it is pretty high latency
    • Kamoso: No capture support
    • k3b: Only used for previews, not transcoding
    • kdenlive: very specialized
    • WebKit: Replaced phonon with QtMMKit, then moved to GStreamer
    • Lots of other apps actually do use it (KTorrent, Digikam, Gwenview)

On Windows

• They use the VLC backend, works great.
• Building, distribution? DirectShow is dead. Don't need it - VLC works! ^^
• GStreamer is a pain to build on Windows and distribute due to the big GTK stack. VLC is just one neat package and statically built.

Capture API

• We don't have any encoders
  • You capture media but its useless.
  • Probably impossible to have an encoding API
  • Might be implemented after we have capturing, which itself would be implemented after the phonon 5 release.
• DVB support will be needed
• Current API is acceptable, no really big modifications needed.

Possible encoding API

• Capture will remain useless until we have an encoding API.
  • Mimetimes, lol.
  • Encoders stream into a Container device, which is a QIODevice (or streams into one)
  • Few encoder options as possible: bitrate, quality (0-100),
• Only a handful of codecs: Maybe 4 audio, 3 useful video. Everything else is silly and useless.
• "Play" or "Transcode"
• Decoding, maybe, for finding fingerprints or visualizations

We need a fluffy object. It outputs unicorns.

Phonon 5 Priorities

1. Drop as much as we can
2. Don't break source compatability as much as possible